Production and coating of metal cans, such as steel or aluminum cans and other hollow cylindrical bodies is a highly mechanized operation involving numerous steps in a long process from the initial metal to the final, properly shaped and coated can. For purposes of this application, aluminum will be used as an exemplary material for cans, however, the invention is not so limited and the term aluminum may be understood to stand in for any customary metal for cans.
Coils of aluminum or steel or other materials are uncoiled from a roll and flattened, then fed through a cupping press which stamps/draws a cup of aluminum or steel material. This goes through a bodymaker press which pulls it upward into a distinctly can-like cup shape, then the bottom is indented, that is, formed into a pressure dome such as customarily seen on the bottom of aluminum and steel beverage cans, bottle containers or other containers. Many beverages sold in cans are carbonated and thus mildly or highly pressurized, the dome shape allows the can to retain its shape despite the pressure. Thereafter the edge of the can must be trimmed since the structure of aluminum or steel metal causes irregularity in the draw and iron process. Note that the D&I process is as follows for beverage and/or food cans: cupper, bodymaker & trim, wash & dryoff oven, decoration followed by decoration cure oven, internal can spray and internal can oven, necker/flanger (bottles may require extra operations at this point), and finally to the palletizer. Note also that most food cans do not get decoration (exterior labels being more common for food cans), so the process is slightly modified to spray, bake, spray, bake, and in use they are vacuum packed.
In the case of three piece cans, they are fed into a blank auto feeder, a welder, side stripper, and oven for curing the stripping, (necker, beader, flanger) and tester, and then the palletizer. This process also may have internal spraying of a coating into the inner surface followed by an oven, if these steps are required.
At this point in almost any type of can operation involving internal coating, the middle part of the can production and coating process begins, and it is this middle part which is of particular interest to understanding the present invention. An understanding of the present invention's benefits requires some understanding of the current bottle necks and operation conditions of the prior art in can production and coating.
The can production and coating facility may normally be laid out on two levels: an upper level and a lower level. The lower level may be ground level, the upper level may be a mezzanine, an upper story of the facility and so on. In practice, the cans must travel from production station to production station while moving up and down the levels.
A can conveyor may convey the cans, en masse, to a decorator machine for decoration. Such can conveyors may be of several types. In particular, some can conveyors may be “mass” can conveyors with many cans arranged to be carried in parallel, for example, something rather like a conveyor belt which is wide enough to carry a number of cans abreast. Other can conveyors can be single file conveyors with a single column of cans in motion. Yet other conveyors may use pins to carry the cans. Conveyors may also have rails to hold the cans in place.
Significantly, such conveyors may convey cans not just horizontally but vertically. Cans may feed through a chute downward, or they may be raised upward if they are placed on a conveyor which exerts a modest negative pressure against the bottom of the can, so that normal ambient air pressure pushes the can against the moving conveyor (this is often thought of as “sucking” the can to the conveyor so that the conveyor may even go straight up, vertically, with the can remaining in place on the vertical conveyor as it moves).
The decorator may be disposed upon the lower level of the facility, with the cans entering from above. The cans exit the decorator and by means of a pin chain or the like may be conveyed, possibly single file, to a pin oven. The pin oven will obviously cure the decorations, however, the pin over will also raise the cans so that they are somewhat elevated above the lower level, possibly as high as the upper level, when the cans depart the pin oven. They may at this point be single file, or in mass, or they may be single file and then conveyed thereafter in mass.
The cans will then descend to the lower level as they enter the horizontal can internal coating machine which is at the heart of the present invention. The cans as they descend leave the vertical orientation and instead feed into something very much like a chute. In the chute the cans lay on their sides, with their axes of symmetry horizontal. The horizontal can internal coating machine will coat the inner surface of the cans as they descend to it. At this point, the cans are of course open at one end but otherwise have their final shape, so the coating operation must occur through the open end of the can.
In the past, the coatings which could be applied to aluminum/steel/alloys at high speed had the disadvantage of slumping. That is, if the coating were applied as one might paint a wall, the coating would thin at the top end and thicken at the bottom end. This is extremely undesirable. Thus the cans were of necessity coated while the cans were in a horizontal position.
The horizontal can internal coating machine would accept the can coming out of the bottom of the conveyor/chute by receiving it into a pocket on the top of a star wheel. The star wheel is vertically oriented, that is, it rotates in a plane which is vertical. The pocket of the star wheel would be dimensioned and configured to receive the horizontal can. The pocket of the star wheel may also have a roller on the side to cause the can to begin rotating within the star wheel.
The star wheel itself is driven by an indexing gear box. The indexing gear box rotates the star wheel by a set angle, the angle equal to the angle between pockets of the star wheel. The indexing gear box then stops the star wheel, and the next can coming down the chute/conveyor may drop into the next pocket. The star wheel is advanced one more index position and stopped and another can drops in the top.
The original can has by this time advanced considerably around the star wheel. At an index position later than the top of the star wheel, it will pass beside a spray gun(s). The spray gun (or guns, two are known in the prior art) will coat the can as it sits in the momentarily motionless star wheel. The roller or similar device will be causing the can to rotate, so the motionless spray gun(s) will quickly coat the entire inner surface of the can. Some steel cans require a spray-bake-spray-bake process because of the products which will be packaged in the steel containers.
When the star wheel is advanced again, the coated can will index forward again by the same angle. In due course, it will move, stopping and starting, until it is on the lower side of the star wheel and gravity begins urging it to fall from the pocket. Devices may cause/assist removing the internally coated can from the star wheel.
Thus in practice, the cans' advance through the horizontal can internal coating machine is actually carried out in a stop-and-go manner, much like a traffic jam on a highway. Like a traffic jam, this places limits on the amount of traffic which can pass through the highway in a given amount of time. In practice, real world prior art horizontal can internal can coating machines can achieve only about 300 to 350 cans per minute (cpm) in internal coating speed of the machine. This is a significant limitation to the can production and coating process.
One obvious way to circumvent this process limitation is to use several horizontal can internal coating machines in parallel, so the facility is likely to be laid out with a number of internal coating machines on the floor of the facility in a row. Each machine will have an individual conveyor/chute descending to it from above carrying an individual row of cans for the machine. From the row of machines, the cans are conveyed horizontally and in mass on the ground floor to an internal bake oven so that the internal coating may be baked.
Emerging from the internal bake oven, the cans are conveyed in mass on a vacuum elevator such as mentioned previously, and the cans are raised in mass to a higher level, possibly as high as the upper level of the facility. Logic would suggest that this is to be taken to another station in the production process which is located on the upper level. However in point of fact, the cans must simply be fed vertically downward to the next step in the process, the necker, rather in the same manner in which they had to be fed vertically downward to the horizontal internal coating machine.
Thus the cans emerge from the internal bake oven, are raised, nothing is done to them at the higher level, and then they are lowered back to the ground level to go to the necker. The vacuum elevator or similar conveyor device is thus needed simply in order to feed the necker properly.
The later steps in the process may then be carried out from the necking forward. The can may be flanged, inspected, and palletized open ended. The beverage/food maker's facility may be the site of filling and seaming of the lid onto the can.
Turning to FIG. 1A, an exemplary PRIOR ART star wheel and horizontal can internal coating machine may be seen. Star wheel 902 accepts can 904 as it is descending (arrow 910 showing descent from a high level, a mezzanine, upper story, etc). The stop-and-go motion of star wheel 902 is depicted by broken arrow 908. When the star wheel 902 rotates by one position and stops, spray gun 906 may spray the stationary can beside it.
FIG. 1B shows the exemplary PRIOR ART from the side, showing that the plane of rotation of star wheel 902 is in fact vertical. Spray gun 906 may be seen to be spraying 914 can 904 as can 904 sits stationary on the momentarily stationary star wheel 902.
FIG. 1C also shows this PRIOR ART device in a limited isometric view. Obviously, there is a time requirement for the spraying to occur. While this time may be fairly short (for example a few hundred milliseconds or less) it is obvious that the can rotate in one place, within the pocket of the star wheel, while the star wheel itself must sit still so that the body may be sprayed for that duration. Then the star wheel must spin by one index position, taking further time. The end result is that a prior art device, as discussed previously, can achieve a coating capacity of at most around 300 to 350 cans per minute under optimal conditions.
FIG. 2 shows the PRIOR ART production and coating facility, at least through the middle stage. As can be seen, there are two levels 920 and 922. Pin oven 924 raises the cans to the upper level 922, after which they are lowered again via chutes/conveyors 926 down to the horizontal can internal coating machine 928 which as can be seen has a vertical star wheel processing the cans. At the new lower level, the cans are conveyed and raised as necessary to the internal bake oven 936 to bake the internal coating just applied. The cans then are raised from the internal bake oven 936 by means of a vacuum or similar elevator previously discussed (not shown). This piece of equipment is present simply in order to raise the cans so that they can then be lowered into necker 934 where they receive their necking and flanging process.
One final issue faced by such facilities is the emission of volatile organic compounds by the horizontal can internal coating machine and by the coatings themselves after they have been applied but before the cans are baked and the coatings solidified. This occurs on the conveyor which runs from the horizontal can internal coating machine to the internal bake oven.
Turning now to more specific and detailed prior art, U.S. Pat. No. 2,103,270, “CAN SPRAYING MACHINE”, in the name Murch, dated Dec. 28, 1937, teaches this horizontal internal coating machine. Obviously the machine is spraying cans which are horizontal, while the plane of rotation of the star wheel 11/12 is vertical. The cans “a” must descend chute 16/17 to reach the stationary first index position (marked by can “A”), before rotating to index position (marked by “B”) and then sitting still again, and so on around until they may depart by chute 125. The process is clearly vertical so that the cans may be horizontal.
The machine of the Murch disclosure does teach that the interior of a horizontally disposed can or container can be sprayed or coated in a manner building up the final coating in stages and/or on different sections of the inner surfaces to that an even and unbroken coating results, despite the tendency of the coating to slump. At that time, filing in 1934, cans were normally of materials other than aluminum.
By the late 1950's, cans for beer had been known and the Adolf Coors Company first put beer into an aluminum can rather than a steel can or the like. This proved to be immensely popular and other companies followed, developing the pull tab top and other refinements.
One Coors patent is in the name of Hartmeister et al, dated Jul. 1, 1969, U.S. Pat. No. 3,452,709 for “MACHINE FOR COATING INTERIOR OF CONTAINERS”. This device shows horizontally oriented cans 28 sliding down chute 29 to star wheel 15. Star wheel 15 is seen to be rotating and can 27′ (one index position after the top) is seen to be counter-rotating due to frictional engagement. Once again, the star wheel is seen to be vertical in order to provide horizontal pockets so that the rotating cans can be held horizontally.
This patent relates to a machine for coating interior surfaces of metal cans with lacquer and/or other protective coatings. The machine is particularly adapted for coating the interior surfaces of fragile cans (such as aluminum cans) without damage to the cans.
U.S. Pat. No. 3,697,313 issued in the name of Nordson for “METHOD OF SPRAYING CLOSED END CANS” (Oct. 10, 1972), taught that a can could be spun while a stationary spray gun sprayed into it. By spinning the can, an asymmetrical pattern could nonetheless coat the entire can interior.
U.S. Pat. No. 4,186,225 in the name of Smith et al for “METHOD OF COATING THE INTERIOR SURFACES OF A HOLLOW ARTICLE” (Jan. 29, 1980), teaches a two layer spraying technique in which there is no intervening drying or baking step, the second layer is thus applied wet onto the still wet first layer. Once again, this patent teaches spinning of the can (1000 to 3000 RPM), the use of stationary spray guns, and so on.
U.S. Pat. No. 4,233,932 in the name of Blakeslee issued Nov. 18, 1980 for “CONTROLLED DISPERSION OF COATINGS” teaches that the sprayer nozzle might spin, that is, spin on the axis of the spray gun nozzle itself. It does not teach that the gun may move on a spinning turret.
U.S. Pat. No. 5,246,300 issued to Jensen on Jan. 20, 1981 for “CAN TRANSPORT” once again shows a vertically oriented star wheel designed to hold cans horizontally, that is, another horizontal coating machine. The cans drop in to the star wheel from a chute coming down from above, and fall from the star wheel at the bottom.
EP 0568365 B1, Sep. 18, 1996 (filing Apr. 29, 1993) for INSTALLATION AND PROCESS FOR CLEANING A SPRAY NOZZLE, in the name of Wayru et al (a Nordson patent) points out another problem with can interior coating machines. The nozzles of spray guns become fouled with use, in particular, the nozzles become fouled due to periods of interrupted use. If a nozzle is used to spray a can interior and then the nozzle is unused for a short time while a star wheel rotates a new can underneath, the nozzle becomes fouled more quickly than if the nozzle is used continuously or in longer time segments.
It would be preferable to provide a novel and nonobvious design which allows can production to exceed, even dramatically exceed, the present day practical limit of around 300-350 CPM imposed by the start-stop nature of the spray process.
It would be desirable to provide a method of allowing spray guns to spray longer into each can, without slowing down production.
It would further be desirable to provide a method of reducing the number of can coating machines required on a production line.
It would yet further be desirable to provide an improved facility layout which minimized the number of times cans must be moved from a lower level to an upper level and vice-versa, thus reducing the number of conveyors, vacuum conveyors and the like which the line required.
All these advantages and more may be attained by means of the present invention, which is described in greater detail below and illustrated in the accompanying diagrams.